Despite tremendous strides in transplantation over the past 40 years, with great advances in short-term graft survival, long-term survival is comparatively poor. This is likely due to the fact that immunosuppressive strategies, though clearly improved over the years, are not tolerogenic. True transplantation tolerance is likely to arise not from improved immunosuppression, but from improved understanding of the normal mechanisms which generate and maintain self-tolerance, and the ability to manipulate these mechanisms for the prevention and treatment of transplant rejection. Recognizing the similarities between the immune response to transplanted tissues and autoimmune syndromes such as multiple sclerosis and diabetes mellitus, it is clear that approaches for transplantation tolerance are applicable for the treatment of autoimmune disorders as well. Our approach is based on the premise that mechanisms which regulate peripheral tolerance may prove most easily exploited to generate tolerance to self and foreign antigens in adults. The overall theme is that restricted delivery of costimulatory signals and regulation of the cytokine milieu are key components of this process. The overall goals of project #1 are understand the effector mechanisms of systemic tolerance induced by APCs which have been modified to present antigen without delivering costimulatory signals. This work will begin in the autoimmune EAE model, but then, after defining immunogenic allopeptides in mice, it will be extended to a murine transplant model. The overall goals of project #2 are to characterize and analyze the use of differing costimulatory pathways during the alloimmune response, and to define the mechanisms of action, at a cellular level, of systemic blockade of costimulatory signals. This project will also examine the role of indirect allorecognition in tolerance induction through costimulatory blockade. The overall goals of project # are to evaluation the role of the cytokine milieu during discrete phases of tolerance induction and maintenance. Using costimulatory blockage as a strategy to induce tolerance, this project will define cytokine patterns during differing stages of tolerance induction/maintenance, and use fusion proteins which are cytokine agonist or antagonists to evaluate the role of selected cytokines in the tolerogenic process. Defining the mechanisms by which costimulatory blockage induces immunosuppression in vivo, and refining its use in these models should prove useful in the design and implementation of clinical trials with these agents. In addition, this work will help establish targets for the development of novel tolerogenic approaches.